Planting trees cannot replace cutting CO2 emissions

Growing plants to store carbon from the atmosphere will not offset unmitigated emissions from fossil fuel burning, a new study shows. At best it could support climate policies of rapid and strong emission cuts.

Researchers at the Potsdam Institute for Climate Impact Research (PIK) in Germany have published a new study assessing biomass plantations as a means of removing carbon dioxide from the atmosphere. Plants suck CO2 out of the atmosphere to build their woody roots, stems and leaves, leading some to suggest that this low-tech terrestrial CO2 removal could be combined with high-tech carbon storage mechanisms to offset the emissions caused by burning fossil fuels.

But as the PIK researchers show in their study, biomass plantation cannot remove enough greenhouse gases under the ‘business-as-usual’ scenario of unmitigated fossil fuel burning.

“If we continue burning coal and oil the way we do today and regret our inaction later, the amounts of greenhouse gas we would need to take out of the atmosphere in order to stabilise the climate would be too huge to manage,” lead author Lena Boysen said in a statement.

“In the business-as-usual scenario of continued, unconstrained fossil fuel use, the sheer size of the plantations for staying at or below 2°C of warming would cause devastating environmental consequences.”

The scientists calculated that the required plantations would be so large they would eliminate most natural ecosystems around the world. Even under moderate CO2 emission reductions in line with the Paris Climate Agreement pledges, the biomass plantations would still be so enormous they would threaten agricultural land and put global food security at risk.

They only scenario in which they could place a role is if CO2 emissions are drastically reduced. Growing biomass now in well-selected places with increased irrigation or fertilisation could then support ambitious climate policies. But even here, technologies minimising carbon emissions from cultivation, harvest, transport and conversation of biomass would need to improve worldwide.

“There is no alternative for successful mitigation,” stated co-author Wolfgang Lucht from PIK.


Image credit: Tim Gorman, flickr/Creative Commons

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